1. Field of the Invention
The present invention relates generally to relay output circuits and, more particularly, to a relay output circuit for use in association with a sensor in which the circuit is operable in conjunction with input voltages that vary over a relatively wide range.
2. Description of the Prior Art
Persons skilled in the art of circuit design are aware of several known techniques for adapting a circuit to operate with relative independence with regard to the magnitude of voltage provided to the circuit. For example, it is common for a sensor, such as a photoelectric sensor, to be provided with a circuit that can accept an unregulated DC input voltage ranging from approximately 10 to 30 volts and provide voltage regulation to assure that the sensing circuitry of the device is supplied with a regulated voltage of approximately 6.2 volts DC. This problem becomes slightly more complex if the circuit must control an external device, such as a relay coil, to selectively connect and disconnect an external component in response to the state of a sensed condition. In other words, a photoelectric detector can be configured to close a relay when light is received by its photosensitive component and open the relay when light is not received.
In situations where the input voltage to the circuit can be any magnitude within a relatively wide range, the higher voltage potentials in that range must be handled in a way which does not damage the external device, such as the relay coil, and does not dissipate excessive power in an inefficient manner. If circuit components are selected to be able to withstand the higher levels of power associated with the higher voltage magnitudes at the circuit input, those components would typically be larger and more expensive than similar components which are designed to operate at lower power levels. Therefore, the use of components with larger power ratings is inefficient for both size considerations and cost considerations. It is also important to assure that the external device, such as the wound coil of a relay, is not subjected to excessive current during operation. Otherwise, the life of the coil and associated relay will be significantly shortened.